Patinopecten (Patinopecten) murayamai bisecta Akiyama, 1962
AKIYAMA, M. 1962. Studies on the phylogeny of
Patinopecten in Japan. Science Reports of the Tokyo Kyoiku Daigaku [Section C -
Geology, Mineralogy and Geography], 8 (74): 63-122, pls. 1-8. [p. 87, pl. 1, figs. 1-3]
«Patinopecten (Patinopecten) murayamai bisecta AKIYAMA, subsp. nov.
Pl. 1, Figs. 1 and 3. Shell medium in size and thickness, suborbicular in outline; inequivalved, equilateral except for auricles; apical angle about 110 degrees.
Right valve moderately convex, with 14 elevated, round-topped, unequal radials which are furnished usually with weak radial threads and rarely with conspicuous ones on their backs and flanks; in a few radials is present a deep or shallow furrow on each back of them; interspaces are narrower than ribs themselves but broader on the posterior submargin; periodic concentric striations are conspicuous; anterior auricle furnished with rather deep byssal notch, fine concentric striations and weak radial threads; posterior one also provided with fine, concentric lines and several conspicuous threads; hinge with conspicuous cardinal crura and a rather large resilial pit provided witn distinct ridges on both margins. Left vaive more convex than the right, with 14 elevated, round-topped, unequal radials which are provided with reticulate sculpture on the outer whole surface of the disc; interspaces much broader than radials ; both auricles with fine concentric striations and rveak but distinct radial threads; hinge corresponding to that of the right. Remarks. The present new subspecies is characterized by the right valve with 12-14 elevated radials with sharp demarcation to interspaces. P. bisecta is completely corresponding to P. murayamai from the shell sculpture except for a number of radials. Some pairs of radials stand close to each other across a narrow interspace, which are supposed to be formed by a bifurcation of a radial. Now, if this pair is counted as a radial, it follows that the present subspecies is furnished with 9 radials, some of which are divided into two parts by a deep furrow. From the above mentioned facts bisecta is closely allied to murayamai and, should be ranked as a subspecies of murayamai phylogenetically. It is noteworthy that the new subspecies is yielded from medium sandstone of the Sugota formation while murayamai from granule conglomerate of the same horizon. Comparisons. The present subspecies is allied to P. murayamai murayamai and, P. murayamai ugoensis, but can be distinguished from murayamai by having numerous radials and from ugoensis by having numerous and more elevated radials. P. kimurai yudaensis is also allied species but can be distinguished by the right valve with much narrower radials and the left valve with less elevated radials which are trianguiar in the cross section of them. Type locality. Ogura, Higashi-Yuri-mura, Yuri-gun, Akita prefecture Sugota formation. Reg. no. 17003 (holotype), 17006 (paratype). Distribution. Sugota formation in Akita Prefecture and Kagitori mernber in Iwate Prefecture.» MASAHIKO AKIYAMA, 1962
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M. Akiyama, 1962, plate 1.
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